The present invention concerns methods of making triple decker sandwich coordination compounds and intermediates useful for carrying out such methods.
The storage of information at the molecular level can afford extraordinarily high memory densities. An approach toward molecular-based information storage that involves the storage of data in distinct molecular oxidation states has been developed. (see, e.g., Lindsey, U.S. Pat. No. 6,212,093; Roth, et al. (2000) J. Vac. Sci. Technol. B 18:2359-2364; Gryko, et al. (2000) J. Org Chem. 65:7345-7355; Gryko, et al. (2000) J. Org. Chem. 65:7356-7362; Clausen, et al. (2000) J. Org. Chem. 65:7363-7370; Clausen, et al. (2000) J. Org Chem. 65:7371-7378; Li, et al. (2000) J. Org. Chem. 65:7379-7390; Gryko, et al. (2001) J. Mater. Chem. 11: 1162-1180). Thiol-derivatized redox-active molecules are attached to an electroactive surface, thereby enabling reading and writing to be achieved via electrical methods (Roth, et al. Anal. Chem. submitted). The information storage density can be increased commensurate with the number of available oxidation states of the molecules in a memory storage location.
Among the various classes of molecules examined for information storage, (Gryko, et al. (2000) J. Org. Chem. 65:7345-7355; Gryko, et al. (2000) J. Org. Chem. 65:7356-7362; Clausen, et al. (2000) J. Org. Chem. 65:7363-7370; Clausen, et al. (2000) J. Org. Chem. 65:7371-7378) the triple-decker lanthanide sandwich molecules (Tran-Thi, T. -H. (1997) Coord. Chem. Rev. 160:53-91; Ng and Jiang (1997) Chem. Soc. Rev. 26:433-442) comprised of porphyrinic ligands proved most attractive due to their large number of redox states, reversible electrochemistry, and relatively low oxidation potentials. The triple deckers generally exhibit four oxidation states in the range 0-1.4 V (vs Ag/Ag+), corresponding to the formation of the monocation, dication, trication, and tetracation (Li, et al. (2000) J. Org. Chem. 65:7379-7390; Gryko, et al. (2001) J. Mater. Chem. 11: 1162-1180). A further attraction of this class of molecules stems from the possibility of interleaving the potentials of two triple deckers, thereby achieving as many as eight accessible cationic oxidation states. This approach for molecular-information storage requires the ability to synthesize triple deckers of a given type bearing linkers for attachment to an electroactive surface.
The synthesis of homoleptic porphyrin triple deckers, first reported by the groups of Buchler (Buchler and Knoff (1985) In: Optical Properties and Structure of Tetrapyrroles; Blauer, G.; Sund, H., Eds.; de Gruyter: Berlin, pp 91-105) and Weiss (Buchler, et al. (1986) J. Am. Chem. Soc. 108:3652-3659), employed the reaction of a lanthanide acetylacetonate complex with a porphyrin in refluxing 1,2,4-trichlorobenzene (1,2,4-trichlorobenzene has bp 214xc2x0 C.; the oil bath temperature for these reactions was set at xcx9c230xc2x0 C.). This procedure grew out of a method developed by Horrocks for the preparation of (Por)M(acac) complexes by reaction of a porphyrin with a lanthanide(acac) complex in refluxing 1,2,4-trichlorobenzene (Wong, et al. (1974) J. Am. Chem. Soc. 96:7149-7150; Wong, C. -P. (1983) Inorg. Synth. 22:156-162). The synthesis of heteroleptic (porphyrin/phthalocyanine) triple deckers has been achieved by two distinct procedures, an undirected xe2x80x9creaction-of-monomersxe2x80x9d route and a directed xe2x80x9cmonomer+dimerxe2x80x9d route (vide infra). The former route proceeds as follows: A porphyrin is treated with excess M(acac)3.nH2O in refluxing 1,2,4-trichlorobenzene, affording the porphyrin.M(acac) complex (Moussavi, et al. (1986) Inorg. Chem. 25:2107-2108). The mixture is then treated with a dilithium phthalocyanine under continued reflux. In various applications of this method it has become clear that the product composition depends on the lanthanide, the nature of the substituents on the porphyrin and phthalocyanine, and the ratio of the reactants (Ng and Jiang (1997) Chem. Soc. Rev. 26:433-442). In our hands, the reaction-of-monomers route using Mxe2x95x90Eu afforded two double deckers of composition (Por)M(Pc) and (Pc)M(Pc), and three triple decker complexes of composition (Por)M(Pc)M(Por), (Pc)M(Por)M(Pc), and (Pc)M(Pc)M(Por); the yields of the three types of triple deckers were typically 10-20%,  less than 3%, and 10-14%, respectively, upon chromatographic purification (Li, et al. (2000) J. Org. Chem. 65:7379-7390).
Accordingly, there remains a need for new methods for the rational synthesis of heteroleptic lanthanide sandwich coordination complexes.
A first aspect of the present invention is a half-sandwich coordination complex, useful for the synthesis of triple-decker sandwich coordination compounds, produced by the process of: reacting a precursor complex of the formula XM(R1)2 with a free base porphyrinic macrocycle to produce said half-sandwich complex, wherein X is a halogen, M is a metal (e.g., a metal selected from the group consisting of Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), and R1 is an amide.
The precursor complex may be produced by reacting a compound of the formula MX3, wherein M is a lanthanide metal and X is halogen, with a compound of the formula ZR1, wherein Z is a counter-ion and R1 is an amide, to produce the precursor complex of the formula X-M(R1)2.
Alternatively stated, the present invention provides a half-sandwich coordination complex, useful for the synthesis of triple-decker sandwich coordination compounds, according to Formula (I):
L-M-Xxe2x80x83xe2x80x83(I) 
wherein X is a halogen; M is a metal (e.g., a metal selected from the group consisting of Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), and L is a porphyrinic macrocycle group.
A further aspect of the present invention is a method of making a half sandwich coordination complex, comprising the steps of: reacting a precursor complex of the formula X-M(R1)2, with a free base porphyrinic macrocycle to produce said half-sandwich complex; wherein X is a halogen, M is a metal (e.g., a metal selected from the group consisting of Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), and R1 is an amide.
A further aspect of the present invention is a method of making a triple-decker sandwich coordination compound, comprising the step of reacting a half-sandwich coordination complex as described above with a double-decker sandwich coordination compound, preferably in a polar aprotic solvent, and preferably at a temperature of at least 100xc2x0 C., to produce said triple-decker sandwich coordination compound.
The foregoing and other objects and aspects of the present invention are explained in greater detail below.
The terms xe2x80x9csandwich coordination compoundxe2x80x9d or xe2x80x9csandwich coordination complexxe2x80x9d refer to a compound of the formula LnMnxe2x88x921, where each L is a heterocyclic ligand (as described below), each M is a metal, n is 2 or more, most preferably 2 or 3, and each metal is positioned between a pair of ligands and bonded to one or more hetero atom (and typically a plurality of hetero atoms, e.g., 2, 3, 4, 5) in each ligand. Thus sandwich coordination compounds are not organometallic compounds such as ferrocene, in which the metal is bonded to carbon atoms. The ligands in the sandwich coordination compound are generally arranged in a stacked orientation (i.e., are generally cofacially oriented and axially aligned with one another, although they may or may not be rotated about that axis with respect to one another). See, e.g., D. Ng and J. Jiang, Sandwich-type heteroleptic phthalocyaninato and porphyrinato metal complexes, Chem. Soc. Rev. 26, 433-442 (1997).
The term xe2x80x9cdouble-decker sandwich coordination compoundxe2x80x9d refers to a sandwich coordination compound as described above where n is 2, thus having the formula L1-M1-L2, wherein each of L1 and L2 may be the same or different. See, e.g., J. Jiang et al., Double-decker Yttrium(III) Complexes with Phthalocyaninato and Porphyrinato Ligands, J. Porphyrins Phthalocyanines 3: 322-328 (1999).
The term xe2x80x9ctriple-decker sandwich coordination compoundxe2x80x9d refers to a sandwich coordination compound as described above where n is 3, thus having the formula L1-M1-L2-M2-L3, wherein each of L1, L2 and L3 may be the same or different, and M1 and M2 may be the same or different. See, e.g., D. Arnold et al., Mixed Phthalocyaninato-Porphyrinato Europium(III) Triple-decker Sandwich Complexes Containing a Conjugated Dimeric Porphyrin Ligand, Chem. Lett. 6: 483-484 (1999).
The term xe2x80x9chomoleptic sandwich coordination compoundxe2x80x9d refers to a sandwich coordination compound as described above wherein all of the ligands L are the same.
The term xe2x80x9cheteroleptic sandwich coordination compoundxe2x80x9d refers to a sandwich coordination compound as described above wherein at least one ligand L is different from the other ligands therein.
The term xe2x80x9cporphyrinic macrocyclexe2x80x9d refers to a porphyrin or porphyrin derivative. Such derivatives include porphyrins with extra rings ortho-fused, or ortho-perifused, to the porphyrin nucleus, porphyrins having a replacement of one or more carbon atoms of the porphyrin ring by an atom of another element (skeletal replacement), derivatives having a replacement of a nitrogen atom of the porphyrin ring by an atom of another element (skeletal replacement of nitrogen), derivatives having substituents other than hydrogen located at the peripheral (meso-, xcex2-) or core atoms of the porphyrin, derivatives with saturation of one or more bonds of the porphyrin (hydroporphyrins, e.g., chlorins, bacteriochlorins, isobacteriochlorins, decahydroporphyrins, corphins, pyrrocorphins, etc.), derivatives obtained by coordination of one or more metals to one or more porphyrin atoms (metalloporphyrins), derivatives having one or more atoms, including pyrrolic and pyrromethenyl units, inserted in the porphyrin ring (expanded porphyrins), derivatives having one or more groups removed from the porphyrin ring (contracted porphyrins, e.g., corrin, corrole) and combinations of the foregoing derivatives (e.g. phthalocyanines, porphyrazines, naphthalocyanines, subphthalocyanines, and porphyrin isomers). Preferred porphyrinic macrocycles comprise at least one 5-membered ring (e.g., a pyrrole ring).
The term porphyrin refers to a cyclic structure typically composed of four pyrrole rings together with four nitrogen atoms and two replaceable hydrogens for which various metal atoms can readily be substituted. A typical porphyrin is hemin.
The term xe2x80x9carylxe2x80x9d refers to a compound whose molecules have the ring structure characteristic of benzene, naphthalene, phenanthrene, anthracene, etc. (i.e., either the 6-carbon ring of benzene or the condensed 6-carbon rings of the other aromatic derivatives). For example, an aryl group may be phenyl (C6H5) or naphthyl (C10H7). It is recognized that the aryl, while acting as substituent can itself have additional substituents (e.g., the substituents provided for Sn in the various formulas herein).
The term xe2x80x9calkylxe2x80x9d refers to a paraffinic hydrocarbon group which may be derived from an alkane by dropping one hydrogen from the formula. Examples are methyl (CH3xe2x80x94), ethyl (C2Hsxe2x80x94), propyl (CH3CH2CH2xe2x80x94), isopropyl ((CH3)2CHxe2x80x94).
The term xe2x80x9chalogenxe2x80x9d refers to one of the electronegative elements of group VIIA of the periodic table (fluorine, chlorine, bromine, iodine, astatine).
The term xe2x80x9cnitroxe2x80x9d refers to an xe2x80x94NO2 group.
The term xe2x80x9caminoxe2x80x9d refers to an xe2x80x94NH2 group.
The term xe2x80x9cperfluoroalkylxe2x80x9d refers to an alkyl group where every hydrogen atom is replaced with a fluorine atom.
The term xe2x80x9cperfluoroarylxe2x80x9d refers to an aryl group where every hydrogen atom is replaced with a fluorine atom.
The term xe2x80x9cpyridylxe2x80x9d refers to an aryl group where one CR unit is replaced with a nitrogen atom.
The term xe2x80x9ccyanoxe2x80x9d refers to a xe2x80x94CN group.
The term xe2x80x9cthiocyanatoxe2x80x9d refers to an xe2x80x94SCN group.
The term xe2x80x9csulfoxylxe2x80x9d refers to a group of composition RS(O)xe2x80x94 where R is some alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group. Examples include, but are not limited to methylsulfoxyl, phenylsulfoxyl, etc.
The term xe2x80x9csulfonylxe2x80x9d refers to a group of composition RSO2xe2x80x94 where R is some alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group. Examples include, but are not limited to methylsulfonyl, phenylsulfonyl, p-toluenesulfonyl, etc.
The term xe2x80x9ccarbamoylxe2x80x9d refers to the group of composition R1(R2)NC(O)xe2x80x94 where R1 and R2 are H or some alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group. Examples include, but are not limited to N-ethylcarbamoyl, N,N-dimethylcarbamoyl, etc.
The term xe2x80x9camidoxe2x80x9d refers to the group of composition R1CON(R2)xe2x80x94 where R1 and R2 are H or some alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group. Examples include, but are not limited to acetamido, N-ethylbenzamido, etc.
The term xe2x80x9cacylxe2x80x9d refers to an organic acid group in which the xe2x80x94OH of the carboxyl group is replaced by some other substituent (RCOxe2x80x94). Examples include, but are not limited to acetyl, benzoyl, etc.
In preferred embodiments, when a metal is designated by xe2x80x9cMxe2x80x9d or xe2x80x9cMnxe2x80x9d, where n is an integer, it is recognized that the metal may be associated with a counterion.
The term xe2x80x9csubstituentxe2x80x9d as used in the formulas herein, particularly designated by S or Sn where n is an integer, in a preferred embodiment refer to redox-active groups (subunits) that can be used to adjust the redox potential(s) of the subject compound. Preferred substituents include, but are not limited to, aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, amido, and carbamoyl. In preferred embodiments, a substituted aryl group is attached to a porphyrin or a porphyrinic macrocycle, and the substituents on the aryl group are selected from the group consisting of aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, amido, and carbamoyl. Additional substituents include, but are not limited to, 4-chlorophenyl, 4-trifluoromethylphenyl, and 4-methoxyphenyl.
All United States patent references cited herein are to be incorporated by reference herein in their entirety.
Porphyrinic macrocycles as described above are known. Particular examples are given in U.S. Pat. No. 6,212,093 to Lindsey. Porphyrinic macrocycles may be converted to free base form in accordance with standard techniques for the displacement of coordinating metals. Examples of suitable porphyrinic macrocycles include but are not limited to compounds of Formula X and compounds of Formula 
wherein:
K1, K2, K3, K4, K5, K6, K7, and K8 are independently selected from the group consisting of N, O, S, Se, and Te (preferably N); and
S1, S2, S3, S4 S5, S6, S7, S8, S9, S10, S11, and S12 are independently selected substituents each selected from the group consisting of H, aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, imido, amido, and carbamoyl.
In addition, each pair of S1 and S2, S3 and S4, S5 and S6, and S7 and S8, may independently form an annulated arene (e.g., selected from the group consisting of benzene, naphthalene, and anthracene), which annulated arene may in turn may be unsubstituted or (e.g., substituted one or more times with a substituent selected from the group consisting of H, aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, imido, amido, and carbamoyl).
Metals xe2x80x9cMxe2x80x9d used to carry out the present invention are, in general, lanthanides such as Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu (preferably Ce, Pr, Nd, Sm, or Eu, and most preferably Ce or Eu).
Precursor complexes of the formula XM(R1)2 used to carry out the present invention may be produced by reacting a compound of the formula MX3, wherein M is a lanthanide metal and X is halogen, with a compound of the formula ZR1, wherein Z is a counter-ion and R1 is an amide, to produce the precursor complex of the formula X-M(R1)2. Suitable amides R1 are generally of the formula NR2R3, wherein R1 and R3 are each independently selected from the group consisting of C1-C6 alkyl, and silyl. Particularly prefered are disilylamides such as xe2x80x94N(SiMe3)2. Any suitable counterion may be employed, including but not limited to Cl, Br, and I. The reaction may be carried out with the same solvents as described below (e.g., glyme solvents), and may be carried out at any suitable temperature, such as room temperature or 0xc2x0 C.
A half sandwich coordination complex of the present invention is made by reacting a precursor complex of the formula X-M(R1)2 with a free base porphyrinic macrocycle to produce said half-sandwich complex. In general, and as described above, X is a halogen, M is a metal (e.g., a metal selected from the group consisting of Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), and R1 is an amide. The reaction may be carried out in any suitable organic solvent (generally polar), but is typically carried out in a nonaqueous solvent, and is preferably carried out in a polar aprotic organic solvent. Particularly suitable are glyme solvents (solvents comprising multiple alkyl ether units, and generally having a boiling point between 100xc2x0 C. and 200xc2x0 C.), such as bis(2-methoxyethyl) ether. The reacting step may be carried out at any suitable temperature, but is preferably carried out at a temperature of at least 100xc2x0 C., and is preferably carried out at a temperature of 200xc2x0 C. or less. The reaction may be carried out in an inert atmosphere, may be carried out under standard dry conditions, and may be carried out in any suitable apparatus such as a Schlenk apparatus.
Without wishing to be bound to any particular theory of the invention, it is believed the foregoing process provides a half-sandwich coordination complex according to Formula (I):
L-M-Xxe2x80x83xe2x80x83(I) 
wherein X is a halogen; M is a metal and L is a porphyrinic macrocycle group as described above. Of course, this is an intermediate compound, and the particular structure of this compound is not critical to carrying out methods of synthesizing the triple-decker compounds described herein.
The half-sandwich coordination complexes synthesized as described above may be used to make triple-decker sandwich coordination compounds by reacting a half-sandwich coordination complex as described above with a double-decker sandwich coordination compound (e.g., a heteroleptic or homoleptic double-decker sandwich coordination compound), preferably in a polar aprotic solvent, and preferably at a temperature of at least 100xc2x0 C., to produce the triple-decker sandwich coordination compound. Preferably at least one of the three porphyrinic macrocycles involved in the reaction (one in the half-sandwich coordination complex; the other two in the double-decker sandwich coordination compound) is different from the others, so that the triple-decker sandwich coordination compounds so made are heteroleptic sandwich coordination compounds. Since these reactions may be carried out in a one-pot fashion, the reaction conditions for this step may be essentially the same or the same as the reaction conditions described above for synthesis of the half-sandwich coordination complexes. The triple decker sandwich coordination compounds may be purified for subsequent use in accordance with known techniques. The reaction may be carried out under essentially the same conditions described above, preferably under dry conditions.
Triple-decker sandwich coordination compounds produced by the methods of the present invention can be used for any purpose, including but not limited to the manufacture of high density memory devices as described in U.S. Pat. No. 6,212,093 to Lindsey.
The present invention is explained in greater detail in the following non-limiting Examples.